Method for the manufacture of centrifugally cast tubular metal articles



Jan. 24, 1956 Filed July 29, 1954 ETAL METHOD FOR THE MANUFACTURE OF CENTRIFUGALLY F. H. GOUPLAND, JR. 273 ,69

CAST TUBULAR METAL ARTICLES 4 Sheets-Sheet l INVENTOR E-ankli CozyvlanaiJr Edwin, H. Phelps. John M Crawford, Kenneth R Daniel. W, M am )ATTORNEYS Jan. 24, 1956 F. H. COUPLAND, JR. EI'AL 297319599 METHOD FOR THE MANUFACTURE OF CENTRIFUGALLY CAST TUBULAR METAL ARTICLES 4 Sheets-Sheet 2 Filed July 29, 1954 INVENTORS flank H Cozgplandgfi Eda/Ln H Phelps. John M. Crazy 'or'd. Kenneihfl Daniel 6 am, Mm, Km

ATTORNEYS 1956 F. H. COUPLAND, JR.. mm. 2,731,690

METHOD FOR THE MANUFACTURE OF CENTRIFUGALLY CAST TUBULAR METAL ARTICLES 4 Sheets-Sheet 3 Filed July 29 1954 m w W w mfim O l n W wwu J COPGB H M W I n 9 $1 W4 53k 1956 F. H. COUPLAND, JR.. ETAL 2,731,690

METHOD FOR THE MANUFACTURE OF CENTRIFUGALLY CAST TUBULAR METAL ARTICLES Filed July 29, 1954 4 Sheets-Sheet 4 fiigwigmga INVENTORS Frank. H Cozgnlanre l bdwr'n 1-1. John/ M Cram/01d. Xennei'h R. Daniel.

ATTORNEKS METHOD FOR THE MANUFACTURE OF CEN- TRIFUGALLY CAST TUBULAR METAL- AR- TICLES Frank H. Coupland, Jr., Edwin H. Phelps, John M. Cranford, and Kenneth R. Daniel, Birmingham, Aim, assigners to American Cast Iron Pipe Company, Birmingham, Ala., a corporation of Georgia Application July 29, 1954, Serial No. 446,488

18 Claims. (Cl. 22-2005) This invention relates to the manufacture of centrifugally cast tubular metal articles, and is particularly concerned with an improved method for centrifugally casting iron and steel pipe, tubing and similar hollow bodies of generally cylindrical form.

Inasmuch as the invention is especially well adapted to the production of cast iron pipe, the following disclosure will be directed primarily to this particular application of the inventive concept. By so doing, however, it is not intended to limit the scope of the invention to the centrifugal casting of cast iron pipe, because it will be obvious that it has equal utility in the manufacture of other types of hollow metal castings.

Heretofore, there have been in general use in the industry only two different methods of centrifugally casting cast iron pipe; the Sandspun method employing a sand mold formed by ramming green sand around a pattern inside a vented metal flask, and the de Lavaud process in which an unvented metal mold is used.

In the Sandspun procedure, the sand mold must be made relatively thick, two inches being a representative thickness, in order to facilitate ramming and also prevent the molten metal from being forced out through the vent holes which are provided in the metal flask to permit ready escape of the water vapor and other gases formed during the casting operation. The use of sand molds requires an extensive amount of mechanical equipment for storing, supplyingand reconditioning the sand, ramming the sand into the flasks, maintaining the flasks and patterns in properly centered positions, and cutting out the sand before stripping the cast pipes from the molds. Considerable labor is also expended in performing the various manual operations necessary in ramming and stripping the molds. These disadvantages of the sand mold process are offset to a substantial extent by the fact that the resulting castings have the desirable characteristics of a typical sand cast gray iron structure and do not require annealing.

In the. de Lavaud method, the'metal mold is normally equipped with a jacket through which water is circulated to reduce the mold temperature produced by the rapid transfer of heat from the molten iron, and is also usually provided with a relatively thin inner coating or facing of suitable composition, such as dry powdered ferro-silic'on or a water suspension of 'such refractory materials as silica flour and bentonite. In most cases, however, such mold coatings are ineffective protection against heat checking, and do not retard the freezing rate sufli'ciently to prevent chilling of the iron. A subsequent annealing treatment is therefore necessary to reduce the hardness and brittleness of the as-cast product of the de Lavaud method. In metal mold casting, it is normally impos- Sible to vent the mold due to the surrounding water jacket and because the liquid iron would flow out through the 'vent holes, or plug them up, during the casting operation. Consequently, it is one of the limitations of the de Lavaud process that the mold facing used may not contain gas-forming materials, because the only available 'ice path for escape of the gases is through the freezing metal with the-resultant danger of forming blowholes and leaks in the casting. The difliculty of providing an adequate protective coating on a non-vented metal mold Without causing trouble due to gas formation in the coating also accounts for the excessively high maintenance and replacement costs which are incurred in the use of metal molds. Compared with the sand mold process, the principal advantages of the metal mold procedure reside in the relatively higher rate of production per casting machine which results from the rapid rate of solidification of the poured metal, and the fact that it is not necessary to form a new mold for each casting.

The process of the present invention successfully combines the advantages and eliminates the disadvantages of the previously known rotary sand mold and metal mold procedures by providing a novel method of forming and using sand lined, vented metal molds to produce high quality unchilled castings rapidly and efiiciently, at low cost and with substantially less capital investment than is required for other centrifugal installations.

The new method is characterized by the use of a vented metal mold having a smooth, uniformly hard, bonded refractory lining of self-sustaining character which is rapidly and accurately formed by a carefully controlled centrifugal procedure, and which, while of substantially less thickness than the sand molds of the prior art, is effective both to avoid unduly rapid freezing of the casting metal and to protect the metal mold against overheating and wear. The mold lining is composed of a mixture of silica sand or other granular refractory and a dry thermosetting resin which, when heated to a predetermined temperature by the extraction of heat from the mold wall, forms a homogeneous, strongly bonded refractory capable of adhering tenaciously to the inner surface of said wall. Once the sand-resin mixture has fused and set, it constitutes a smooth, dense coating on the interior of the mold which will readily withstand the washing action of the molten metal during casting, but, after the casting has frozen, will disintegrate as a result of burning of the resin under the heat of the solidified metal so as to permit rapid, easy stripping of the casting from the mold. Lined molds of this character may be prepared in quantity with the use of relatively little sand, and, being non-hygroscopic, may be held in storage for indefinite periods of time before being used for casting.

The casting step of the method of the present invention is generally similar to that of the prior Sandspun process, but is characterized by a substantially shorter casting time than that previously obtainable, due to the fact that the resin bonded lining of the mold is very much thinner than the ordinary sand mold and therefore freezes the casting much more quickly. As compared with the de Lavaud casting operation, the present method has the advantage that the gases created in the mold lining may readily escape outwardly through the vents of the mold and are not forced inwardly through the molten metal, the vents being covered by a strong but permeable lining which permits passage therethrough of the gases but effectively prevents the molten metal from flowing into the vents.

Gray iron castings produced by the new process are characterized by a distinctive improved structure in compari'son with gray iron castings produced by other centrifugal methods. Ordinary sand mold centrifugal processes produce a relatively coarser grained gray iron with large graphite flakes which, when machined to a fine finish, may show a somewhat rough pitted surface appearance. The usual metal mold centrifugal processes produce a chilled outer surface which can be softened by annealing, but the resultant annealed structure contains free ferrite and is consequently undesirable for many applications. By

the process of the present invention, using a resin-sand mold lining of controlled thickness, there is obtained in the as-cast state an unchilled fine grained pearlitic iron with flake graphite in random distribution, a structure which has been found to be the most desirable for many applications, particularly those where resistance to wear is essential.

It will be apparent from the foregoing general description that the principal object of this invention is to provide an improved process for making centrifugally cast metal pipe and similar articles in sand lined metal molds, which process produces clean, smooth castings having generally the same properties as those obtainable by the Sandspun method, but does so more quickly, at lower cost and with substantially less equipment and labor than the prior procedure. Other objects, including the provision of a new method of centrifugally lining a vented metal mold with a thin coating of a resin bonded refractory, will appear more fully upon consideration of the detailed description of the invention which follows. In this connection, it is to be expressly understood that the specific mold lining and pipe casting procedures hereinafter described and the particular apparatus shown in the accompanying drawings are illustrative only and are not to be construed as representing the full scope of the invention defined in the appended claims.

In the drawings, wherein like reference characters indicate like parts throughout the several views:

Figs. 1 and 2 are diagrammatic plan and front elevation views, respectively, of an installation for producing centrifugally cast cast iron pipe in accordance with the present invention, certain of the elements having been omitted in the interest of simplicity;

Fig. 3 is a diagrammatic end elevation of the mold lining apparatus of the system of Figs. 1 and 2, also show ing the pouring ladle and associated equipment at the casting station;

Fig. 4 is a side view, partially in section, of one embodiv ment of mold adapted to carry out the invention, this view also showing the trough by which the sand-resin mixture may be introduced into the metal mold in the position occupied thereby just before the mixture is dumped into the rotating mold;

Fig. 5 is an enlarged cross section of the metal mold and trough taken substantially on line 5-5 in Fig. 4;

Fig. 6 is a cross section similar to Fig. 5, but showing the trough in inverted position;

Fig. 7 is a partially sectioned side view similar to Fig.

4 showing the sand lined mold as it exists just prior to pouring of the molten metal;

Fig. 8 is an enlarged half axial section of the bell end of the metal mold of Fig. 4 showing the removable metal insert for shaping the outer surface of the bell of the pipe and the means by which said insert is detachably fixed in place;

Fig. 9 is an axial sectional view, on an enlarged scale,

able ladle by a relatively short pouring trough of conventional construction. In making extra long or extra heavy pipe, it may be desirable to use a longer trough extending a substantial distance into the mold and to withdraw the trough as the metal is poured to facilitate longitudinal distribution of the charge.

If desired or necessitated by the size and weight of the mold, the mold may be rotated at a uniform speed throughout the casting operation, which speed must be sufficient to form the casting on the mold wall centrifugally as the metal is introduced. This is known as high speed casting and involves a relatively high speed of rotation such as to create centrifugal forces at the inner surface of the mold on the order of to 75.times the force of gravity. For example, in making a 20 pipe by the high speed casting procedure, it is desirable to rotate the mold at from 450 to 500 R. P. M.

If is preferable, however, to introduce the molten iron into the mold while the latter is rotating at a speed below that at which the metal is caused to cover the mold wall by centrifugal force, so that the metal may first distribute itself longitudinally in the form of a trough or slab on the bottom of the slowly spinning mold. Then, as soon as all or the major portion of the charge is in the mold, the rotation is accelerated to a speed at which the metal will distribute itself circumferentially and form the pipe under centrifugal action. This procedure is called low speed casting, and is particularly desirable because any loose particles of the mold lining or impurities in the molten metal, together with the slag, will float on top of the slab lying along the bottom of the mold and will not be trapped against the mold lining or within the wall of the casting.

In utilizing the low speed casting technique in the method of the present invention, to which it is particularly adaptable because the molds provided by the invention are substantially lighter than the sand molds used in the Sandspun process for making pipe of the same diameter, the mold is spun at a relatively low speed of from 20 to 80 R. P. M. while approximately 75 of the molten iron charge is being poured into the mold, and is then very rapidly accelerated, within a period of from 5 to 10 seconds, to a relatively high speed on the order of tenor more times the low speed. For example, in casting a 6" pipe, the mold may be rotated at approximately 50 R. P. M. for about 12 seconds after pouring of the metal begins, during which time 75% of the metal in the ladle is delivered into the mold. The speed is then increased in about 6 seconds to approximately 850 R.'P. M., equivalent to a centrifugal force of about 60 times the force of gravity, and the high speed rotation is continued until the casting solidifies, which takes only about one minute. In the case of a 20 pipe, the mold may be rotated at approximately 20 R. P. M. for the first 20 secof the form of vent embodied in the metal mold of Figs. 7

4 and 7; and

Fig. 10 is a view similar to Fig. 9 showing a modified form of vent.

The method of making a cast iron pipe provided by the present invention comprises a series of coordinated steps performed at succssive stations of a production line system adapted for continuous, closed cycle operation.

In practice, the beginning of the cycle may be taken to be the centrifugal casting step wherein a charge of molten iron is poured into a rotating mold comprising a vented metal mold having a resin bonded sand lining and rotation of the mold is continued until the cast metal solidifies or freezes into the form provided by the mold.

During the casting, the. mold is supported in a substantially horizontal position on, and is rotated by, the motor driven rollers of an ordinary centrifugal casting machine, and the molten iron is delivered into the mold from a tilt- .onds of the casting operation, accelerated during the next '10 seconds to a speed of approximately 400 R. P. M.,

equivalent to a centrifugal force of about 45 times the force of gravity, and then spun at the latter speed for from four to four and one-half minutes while the casting freezes. Due to the fact that the resin bonded sand linings of the molds of the present invention are very much thinner than the sand molds of the prior art, the length of time required for the casting step is substantially less than in the Sandspun process, the saving in time being between two and ten minutes per cast, depending upon the size and thickness of the casting, with a consequent increase in production rate.

Since the temperature of the molten iron is in. the neighborhood of 2400 to 2500" F. when it is poured and comes into contact with the mold lining, the heat of the metal quickly burns out the resin in the lining, thus deing is devoid of strength and the pipe is ready to be stripped without any further operation on the lining. I

At the stripping station, the casting is removed from the mold, carrying with it most of the lining in the form of a frangible carbonized crust, and is delivered to a cooling station where the encrusted remains of the lining are removed and the pipe is cleaned with wire brushes or in any other suitable manner. If desired, the burned sand of the old lining may be screened to remove lumps and fines, and then returned to the sand preparation station for reuse. It is desirable to strip the pipe from the mold as quickly as possible after the casting step has been completed in order to prevent excessive heating of the metal mold by the cast metal because, upon completion of the stripping operation, the empty mold is returned to the lining station where it is prepared for the next cast, at which time it is essential that the temperature of the mold wall be within a predetermined range such that the heat therefrom will be suliicient tofuse the new lining into a strongly bonded mass, but not so high as to char any of the resin in the lining. Accordingly, it is preferable to strip the mold within a minute or two after the casting has frozen, and to so time the return of the empty mold to the lining station that normal atmospheric cooling during the return will reduce the outside mold wall temperature to within the range from 300 to 600 F., and preferably to between 350 and 400 F., the permissible limits of said temperature being dependent upon the kind and amount of resin binder used in the lining. If

necessary, artificial cooling may be resorted to in order to reduce the mold temperature to within the desired range between the stripping and lining stations.

If, for any reason, the metal mold is cold when ready to be lined, or its temperature is below the desired minimum, it may be heated in any suitable manner, as by gas torches or in a heating chamber. In normal operation of the method, however, each mold is lined while the metal wall still retains sufiicient heat from the previous casting step to exert the desired melting and polymerizing effect on the resin of the lining mixture.

At the lining station, the metal mold is provided with a relatively smooth, hard, self-sustaining coating adherent to the mold wall composed essentially of a mixture of silica sand, or other granular refractory, and a thermosetting resin, the two ingredients being thoroughly mixed together in proportions of from 95.0 to 98.5% by weight of sand and from 1.5 to 5.0% by weight of resin. While various types of resin binders may be used, a two-stage phenol formaldehyde resin containing approximately of hexamethylenetetramine has been found quite satisfactory and is preferred because it melts and polymerizes when heated to any temperature between 300 and 600 F.', a range within which the temperature of the metal mold may be readily maintained during repeated casting cycles.

The term two-stage phenol formaldehyde resin refers to a resin which is produced by first reacting 'to a controlled degree phenol and a limited amount of formaldehy'de, and then incorporating additional formaldehyde in the resin in the form of hexamethylenetetramine which decomposes on heating to formaldehyde and ammonia. The characteristics of such a resin are its dry powder tans, 'insolub'ilify in water, fusibility above 300 F., and capability after melting of polymerizing to an infusible phase with strong bonding properties. Among the commercially available resins of this type suitable for use in the method of the present invention are Thor 27 8,, manufactured by the Borden Chemical Company, and R436, manufactured by the Barrett Company. This particular type of resin has the further advantage that 'it undergoes a distinctive color change as 'it polymerizes which provides a visual indication of when "the lining has set. Aph'enol furfural resin "containing heiiarnethylenetetrarnine has also been used, but is not as satisfactory as the phenol formaldehyde type in that it does not exhibit the color chan e above mentioned. y H

The sand used for the liningshould be a good quality, Washed silica sand which has been thoroughly dried and then screened to eliminate all foreign matter and provide sand of the grain size and distribution necessary to produce the desired smooth mold finish. Sand having an AFS grain fineness of from 40 to 150 is preferred for the making of cast iron pipe, a typical sand having an AFS grain fineness of with 70% on screens 70 through When casting steel, coarser sand may be used in order to facilitate escape of the greater amount of gas which is generated with the higher castin temperatures or steel. It has also been found that, within the permissible range of grain sizes, the coarser the sand, the rougher the surface of the lining, but the more uniform its thickness. Relatively fine sand, on the other hand, provides a smoother lining, but is apt to result in a wavy surface with a consequent non-uniform thickness. 0

in preparing the lining mixture, carefully Weighed quantitles of the dry, screened sand and "the bonding resin in dry powder form are charged into a suitable inixe'r'cr mulier in the proportions above indicated and thoroughly mixed together, after which the mixture is transferred to a storage bin from which measured quantities are dispensed as the molds are lined. When lining molds for the production of pipe up to about 6 or 8" in diameter, the preferred proportions of the lining mixture are 7.0% sand and 3.0% resin; for the larger sizes of pipe, it is preferable to use 97.5% sand and 2.5% resin. In lieu of a mechanical mixture of dry sand and powdered resin, it is also possible to form the lining of sand which has been coated with liquid resin and then dried,in which event the resin content may be as low as 0.5% of the weight of the coated sand.

The metal molds used in producing pipe in accordance with the present invention are generally similar in construction to the mold flasks heretofore used in the Sandspun process, although differing from the latter in certain important details which will be pointed out hereinafter in connection with the description of the apparatus shown in the accompanying drawings. In general, however, each metal mold consists of a substantially cylindrical tube of cast iron or steel having a wall thickness preferably at least three times the thickness of the casting to be produced, the outer surface of the mold being provided with spinning bands or tires for rotating the mold on the motor driven rollers of the lining and casting machines. One end of the mold may be equipped with a bell shape for casting pipes complete with bells or flanges, the other end being adapted to receive a stop-on" plate or core to prevent the molten metal from running out during casting. The inside surface of the mold which forms the outside contour of the casting may have any shape which will allow the solidified casting to be withdrawn from one end 'of the mold, or a split mold may beYuse dfor producing other contours. The metal mold is preferably vented in order to permit the escape of the gases generated in the lining during casting, particularly when making steel pipe or relatively long pipe of other-metals, although vents may not be essential if the mold is relatively short.

in forming the mold lining, the empty metal mold, .still hot from the-preceding casting or having been otherwise heated to the desired temperature, and with either one or two annular lining stop-off plates attached to its ends, is placed on the rollers of a'suitable spinning mechanism, similar to the conventional centrifugal casting machine, and is rotated while a measured quantity of the loose, dry sand-resin mixture is introduced into the interior of the mold and distributed uniformly along' the axis thereof. If desired, the inside surface of the metal moldtit'ay be blacked or coated with carbon with an acetylenefialne prior to the lining operation. When this is done, "there "is less tendency for the sand of the lining to adhere to the same length as the mold, evenly distributing the mixture over the full length of the trough, insert the trough in the rotating mold, and then quickly invert the trough so as to allow the lining mixture to drop out on the lower portion of the inside surface of the mold wall. immediately after dumping the mixture, the trough is quickly withdrawn from the mold so as to prevent it from absorbing heat which might adversely affect the next lining charge.

After thelining mixture has been delivered into the mold, rotation of the latter is continued to uniformly.

distribute the loose granules of the mixture circumferentially over the inner surface of the mold, and until substantially all of the thermosetting resin has polymerized under the effect of heat extracted from the mold and has bonded the sand particles together to form a relatively smooth, hard refractory lining adherent to the moldwall. When the preferred phenol formaldehyde resin is used, curing or setting of the lining is clearly indicated by its 'change in color from near-white to lemon-yellow or light tan. Should the lining be darker than the desired color, it would indicate that the temperature of the metal mold is above the proper range and that some of the resin in the lining is apt to char and thereby weaken the lining if the mold is permitted to stand for any substantial length of time before being used for casting.

It has been discovered by experimentation that the proper spinning speed of the mold during the lining operation is best determined by the centrifugal force created at the inner surface of the mold wall and by expressing said force in terms of the force of gravity, in accordance with the formula where kg represents a centrifugal force equal to K times the force of gravity, N is the speed of rotation of the mold 'in revolutions perminute and D is the inside diameter of the metal mold in inches. It has also been discovered that,in lining molds of different sizes, differentspeeds and techniques of mold rotation may be employed in order to obtain the desired results.

For example, in lining molds for the production of pipe having diameters in the neighborhood of 6", good results have been obtained by using a two-speed technique; i..'e., first, while the lining mixture is being de- 'livered into the mold and until the particles thereof begin to adhere to the mold wall, maintaining a relatively low spinning speed such as to create a centrifugal force not greater than 0.5 times the force of gravity, and preferably on the order of 0.1 times the force of gravity, so that the particles of the mixture are not held to the mold wall by centrifugal force, but are allowed to roll along the bottom of the inner surface of said wall, and then, after the particles begin to adhere to the mold wall, accelerating to-a speed sufiicient to produce a force not less than 5.0"times the force of gravity, and preferably 8.0 -.times the force of .gravity or higher. a metal mold having an inside diameter of 7", the lining Specifically, with mixture may beintroduced while the mold is spinning at about 35 R. P. M., giving a value of 0.12 g according to the above formula, and after partial adherence is estab- .-lished, the spinning speed may be accelerated to about 300 R. P. M., which is equivalent to 9.0 g.

The advantages of fonning the mold lining while thus controlling the speed of rotation of the mold are several. For example, if the lining mixture is introduced while the mold is rotating more rapidly than permitted by the above limitations, the lining will tend to be rippled and uneven, while if the rotation is too slow in the second stage when the resin is setting, the coating may lack density and be relatively soft. By proceeding in the manner described, a smooth, hard, dense coating of any desired thickness, within the limits hereinafter stated, can be produced. i

Another advantage of this particular lining technique is that it permits the use of a vented metal mold in spite of the fact that the lining is centrifugally formed. If a vented mold is spun too rapidly when the lining mixture is first introduced, the particles thereof may be forced out through the vent holes, resulting in an uneven and nonuniform lining, with a very thin or non-existent coating over each vent hole. By employing the two-speed rotational procedure, small quantities of the lining mixture are permitted to enter and harden in the innermost p'ortions of the vent holes during the initial low speed rotation and thereby effectively seal them against expulsion of sand or resin at the subsequent higher spinning speed. The lining so produced is, however, quite permeable to gas, particularly as the resin burns out during the casting operation, so that the vent holes adequately serve their intended purpose. For example, it has been found that open vents having /is diameter openings into the interior of the metal mold, spaced from 3" to 8" apart, can be efiectively closed and sealed with a permeable refractory coating by the present method.

When the method of the present invention is applied to the casting of pipe of relatively small diameter, such as 2" pipe, the above-described lining procedure may be modified by rotating the mold at a uniform, relatively low speed throughout the lining operation. For example, satisfactory results have been obtained in thelining of molds for casting 2" pipe by rotating the molds continuously during the lining operation at a speed of approximately 50 R. P. M., equivalent to a centrifugal force or about 0.1 times the force of gravity. This procedure provides a lining of uniform thickness and adequate density, but somewhat less smooth than that resulting from the two-speed technique. The desired smoothness may be obtained, however, by the application to the lining of a facing of relatively fine sand, ground coke and resin in the manner hereinafter described.

In lining molds of relatively large diameter, such as those used in the production of 12" pipe and larger, .it is preferable to apply the lining in two separate layers of approximately equal thickness, forming the first layer while rotating the mold at a relatively high speed such as to create a centrifugal force of approximately 50 times the force of gravity or greater, and then forming the second layer at an even higher speed which may be equivalent to a centrifugal force of about times the force of gravity or more. The following tabulation indicates the mold rotational speeds at which the two lining layers may be formed in molds for pipe of the sizes indicated:

Mold Speed in Revolutions Per Minute Pipe Diameter First Lin- Second Linlng Layer ing Layer In this two-stage lining procedure, each layer of the lining is formed separately by placing in the lining trough approximately half of the total amount of lining mixture required to produce the desired thickness of lining, evenly distributing the mixture over the full length of the azamoo trough; inserting the trough inv the rapidly rotating. mold, andthen inverting the troughrso as, to deliver thelining mixture onto the lower portion ofthe inside surface of the mold wall. The second lining layer may be. applied as soon as. the firstlayer. has cured or set, either by rotating the, mold at the higher speed in the same spinning machine, or after transfer of the mold to an adjacent machine. In viewof therelatively high rotational speeds employed, the vent: holes. in. the mold wall should be providedwithcore box. vents of the character hereinafter described and illustrated in Fig. in order to prevent the escape of lining mixture. through the vent holes and consequent. defects. in the lining adjacent said holes.

The twoastage, high-speed lining procedure produces an extremely smooth, hard lining of high density and uniform thickness which, due to the fact that the first lining layer.- is. formed at a lower speed than the second, facilitates stripping of the. casting from the mold because the lining adheres more tightly to the casting than to the mold wall.

While. the thickness of the mold lining may be varied somewhat to produce pipes of different diameters in the samemetal. mold, it has been found preferable in practice to carefully control the lining thickness for best repetitive production. The factors governing. the thickness of the mold. lining have already been indicated in functional terms in the general. description of the invention. Althoughdiameter, metal casting temperature, and other considerations may affect the required lining thickness to someextent, the principal factor determining the optimum value of said thickness is the thickness of the metal castingtohe produced. For example, it has been determined experimentally that for castings having a wall thickness from A" to- /2", a mold lining thickness of from 0.12." to 0.18" meets the requirements most effectively. For thicker castings, thicker linings are desirable. As a useful method of. determining the optimum lining thickness for a casting, of a given thickness, the following empirical formula has been developed:

where T. represents the lining thickness and t is the thickness ofthe casting. Typical values obtained from this formula are. as follows:

Casting Thick- Lining Thickness (t) ness (T) Inches Inches 0. 125 0. 088 0. 25 0. 125 0. 50 0. 177 1. 00 0. 250 2. 00 0. 354

In commercial production, satisfactory results. can be obtained by approximating the optimum values derived from the above formula and using the same lining thickness; for castings of several different wall thicknesses within, a limited range. For example, in casting pipe having diameters of from 12" to 20", wherein the wall thicknesses may vary from about 0.40" to about 0.65 it has. been foundthat a uniform lining thicknessof 0.18" will effectively produce the improved results which are characteristic of the method of the present. invention. When, as in the foregoing example, the lining is formed in two layers, it,will be understood that the liningthickness specified is the combined thickness of. both layers, and that the thickness of each layer may be varied as desired as long as the second layer is at least asthick. as the. maximum irregularity in the surface of the first layer.

, In practice, the desired lining thickness may be readily assured by .first establishing either the weight or the volume of, lining material required to produce that thickness: and then using carefully weighed or volumetrically measured quantities of said material for each lining; in

when themixtureused for the: case of, a two-layer. lining, thesimplest procedure, is to use half, of the. computed weight. or volume of lining material for. eachlayer.v

After the, mold. has been lined: inv the manner, above described and the. lining stop-off plates have, beenremQVed, the. lining. may be provided with a wet facing or blacking in order to close the spaces between the sand grains and give a smoother finish to the casting, When. the, metal to be cast is cast iro n,,the facing may consist of. a water suspension of ground coke and clay; when casting steel, a slurry of silica hour and bentonite is preferred. The facing may be applied in any suitable manner, as by pour.- ing,. spraying or brushingit onto the inner surface of the mold lining. For example, with the apparatus illustrated in. Figs. 1, 2 and 3,, the facing procedure involves pouring the facing into the mold through a funnel while the mold is rotated at a relatively slow speed, withdrawing the funnel and then passing a brushthrough the mold while the latter is rotated at a substantially higher speed so as to uniformly distribute the facing. over the lining surface. The facing operation may conveniently be performed at the lining station using the same mold spinning mechanism as that employed for the lining step. The facing dries relatively quickly after it has been applied, due to the heat of the mold Wall, and burns out when the molten metal is poured during the subsequent casting step.

When the lining is formed. by the one-step, uniform speed procedure described above with reference to the casting of small diameter pipe, it is preferable to face or black the lining with. a dry mixture of relatively fine sand, ground coke. and thermosetting resin so as to provide the lining with a smoother, stronger surface than would result fromthe application ofa wet facing of coke and clay, or silica flour and. bentonite. A suitable. dry facing mixture, may contain from 33 to 50% by weightof silica sand having an AFS grain fineness of and from 50' to 67% by weight of ground coke, plus an amount of resin binder equal to from; 8 to. 12% of the total weight of. the. sand and coke. The resin is, preferably of the same kind as that usedin the lining mixture; The dry facing mixture may be blown into the lined. mold by means. of a suitable nozzle which is moved along the axis of the mold while the latter is rotated at a relatively slow speed by the same mold spinning mechanism as that employed for the lining step. The heat of the mold wall and; lining quickly fuses-the resin of the facing mixture and firmly bonds the sand and coke constituents thereof to the inner surface of the lining,

In lining large diameter molds with the two-stage, highspeedtechnique, it has been found that the. separate facing or blacking operation may be omitted and a more satisfactory casting surface obtained by simply including in the lining mixture used for the second lining layer small amounts of graphite and iron oxide. For example,

the first" layer of the lining has the'preferred portions of 97.5% sand and 2.5% resin, the second layer may consist of 94.75% sand, 2.5% resin, 2.25% graphite and 05% iron oxide. The graphite, like the coke of the separately applied facing mixtures, prevents the molten metal from wetting the sand an d'thus avoids sand-penetration into the outer surface of the casting, while the iron oxide strengthens the lining by reducing its brittleness and increasing its high temperature deformation characteristic, thereby making the lining more resistant to penetration by the molten metal." If desired, the graphite may be used without the addition of iron oxide if the lining is otherwise sufiiciently strong to resist penetration during the casting operation.

Upon completion of the lining and facing operations, the bell end of the mold is fitted with an oil sand socket core of conventional type, also faced with blacking, while the opposite end receives a stop-off plate preferably pro- 'vided with an annular groove facing the space to be oc- 11 composition as the'mold lining adapted to prevent chilling of the end of the casting. The mold is now ready to repeat the cycle beginning with the casting steppreviously described, and may therefore be transferred directly to the casting station. On the other hand, since the lining has no affinity for water, the lined mold of the present invention can be prepared far in advance of casting and kept for an indefinite period of time before use, if so desired.

Turning now to the drawings, Figs. 1, 2 and 3 show in diagrammatic form one arrangement of mechanism which may be used for the production of cast iron pipe in accordance with the present invention. As shown, the installation comprises a mold lining and facing station 11, a casting station 12 and a stripping station 13 arranged in production line fashion and interconnected by means for transporting the molds 14 from one of said stations to another in a closed cycle, together with a fourth station 15 to which the stripped pipes 16 are delivered for cooling, cleaning and storage.

The mold lining and facing, casting and stripping stations are connected by a set of parallel rails 17 which slope downwardly at a slight angle from right to left as viewed in Figs. 1 and 2 so that the molds may be transferred from the lining and facing station 11 to the casting station 12,

and from the latter to the stripping station 13 by simply rolling them along the rails under the influence of gravity. The rails 17 also extend beyond the stripping station 13 to an elevator 18 adapted to raise the empty metal molds after the cast pipes have been stripped therefrom and deliver them to a second set of rails 19 (omitted in Fig. l in the interest of clarity) which are positioned directly above the rails 17 of the lower run and slope in the opposite direction so as to roll the molds to the right in Figs. 1 and 2 and return them to the lining and facing station 11 with the aid of a lowering device or drop 20. When the drop 20 moves downwardly from its upper position shown in Fig. 2, the mold carried thereby is deposited on the right-hand ends of the rails 17 which extend outwardly beyond the lining and facing station 11 and on which the mold may roll to said station.

The mold lining and facing station 11 includes three sets of mold rotating rollers 21, 22 and 23 which are commonly drivable by a manually controlled, variable speed motor 24 through a suitable belt or gear transmission. The rollers 21, 22 and 23 are so arranged that one mold may rest on and be rotated by rollers 21 and 22, while another mold may be simultaneously supported and rotated at the same speeds as the first one by rollers 22 and 23. Any suitable means (not shown) may be provided for delivering the molds to and ejecting them from the roller supported positions indicated in Figs. 1 and 2. Axially aligned with the metal mold 14 resting on rollers 21 and 22 is the apparatus for preparing and delivering into the rotating mold the sand-resin mixture for forming the mold lining. As shown, this apparatus in cludes a muller 25 in which the desired proportions of sand and resin are thoroughly mixed in the predescribed manner, and an elevator 26 which carries the mixture upwardly from the muller 25 and delivers it into a storage bin 27. From the storage bin, charges of the sand-resin mixture may be withdrawn into a measuring hopper 28 which is so designed as to hold the desired amount of mixture necessary to produce a lining of given thickness. Beneath the hopper 28 and substantially coaxial with the mold on rollers 21 and 22 is a movable lining trough 29 which, as indicated in Figs. 4, 5 and 6, may be substantially U-shaped in cross section and provided with vertical division plates 30 and 31 defining the ends of the portion of the trough into which the measured quantity of mixture is delivered from the hopper. Any suitable means, such as a strike or a leveling vibrator, may be used for evenly distributing the sand-resin mixture throughout the length of the trough.

The trough 29 is so mounted that it can be moved quickly into and out of the mold 14 as the latter is rotated on rollers 21 and 22, for which purpose the trough may be slidably supported in suitable fixed guides or,- as shown in Figs. 1 and 3, mounted on a movable carriage 32 running on rails 33. If desired, a trunnion 34 may be provided at the end of the lining machine opposite the carriage 32 for receiving a cylindrical extension 35on the end of the trough 29 (see Fig. 4) so as to ensurethat the trough is properly supported and centered axially with re spect to the mold. The mounting of the trough, whether it be in fixed guides or on the carriage 32, is such that, after the trough has been inserted in the spinning mold, it may be quickly inverted as indicated in Fig. 6 to dump the sand-resin mixture onto the bottom portion of the mold wall and then rotated back to its original position and rapidly withdrawn from the mold. j

As the metal mold approaches the lining station on the rails 17, or after it has been placed on the rollers 21 and 22 but before their rotation is begun, an annular lining stop-off plate 36 (see Fig. 4) is detachably fitted to the spigot end of the mold for preventing loss of the lining mixture and forming a square edge at the end of the lining. If desired, a similar stop-off plate 37 may be fitted at the bell end of the mold, although this is not normally necessary.

Assuming that the lining is to be formed by the singlestage, two-speed procedure, the mold is placed on rollers 21 and 22 and the motor 24 is started and so regulated as to rotate the mold at a relatively low speed, equivalent to a centrifugal force of less than 0.5 times the force of gravity. After the proper quantity of sand-resin mixture has been delivered fromthe measuring hopper 28 to the lining trough 29 and has been evenly distributed aiong the length thereof, the trough is quickly moved into the rotating mold, inverted to dump the mixture onto the bottom of the latter, and immediately withdrawn. As soon as the sand grains begin to stick to the mold wall due to melting of the resin, the operator adjusts the control circuit of motor 24 to accelerate the mold rotation to a speed such that the centrifugal force at the inner surface of the mold Wall increases to more than 5.0 times the force of gravity. High speed rotation is then continued until the change in color of the lining indicates that the resin has polymerized and the lining has cured or set, whereupon the motor 24 is stopped, the lining stop-off plates 36 and 37 are removed, and the lined mold is transferred from rollers 21 and 22 to rollers 22 and 23 for the facing step. It will be obvious that rollers 21 and 22 may also be used to rotate the mold while forming the lining by either the one-step, uniform speed procedure, or the two-stage, high-speed technique, by appropriate adjustments of the control circuit of motor 24.

Although various means may be employed for applying the desired carbon facing to the lining, the mechanism illustrated consists of a blacking funnel 38 and a brush 39. As shown, the funnel 38 is detachably fixed to a post 40 by a mounting plate 41, the post 40 being pivotally supported for movement about a vertical axis in a base 42 so that the funnel may be swung to and from a position in which the outlet thereof extends into the bell end of the mold, as indicated in broken lines in Fig. 1. The brush 39, which has a handle coaxial with and at least as long as the mold, is mounted on a carriage 43, the latter being movable on rails 44 so that the brush may be readily passed through the rotating mold from one end to the other. While the lined mold on rollers 22 and 23 is being rotated at low speed, simultaneously with the next mold in line which is then undergoing the first portion of the two-speed lining operation previously described, the fun nel 38 is moved to the broken line position of Fig. 1 and the facing slurry is introduced into the mold by pouring it through the funnel. As soon as all of the facing is in the mold, the funnel 38 is withdrawn and, as the rotation of the mold is accelerated concurrently with the latter portion of the lining operation on the next mold, the brush 39 is moved into the 'mold and so manipulated as to dis- 13 tribute fading n g fi Yet hi nr j i j 't he lining. Alternatively, the hahdleof the brush3 9 may be hollow and serve asa condhlt for introducing the facing suspension into the mold through or just ahead of the brush.

When the mold is rotated by rollers 21 and 22 at a uniform speed throughout the lining operation, it is apparent that rollers 22 and 23 will likewise provide a uniform rotational speed duii'ng the facing step. Although the roller arrangement illustrated is not adapted to carry out simultaneously both stages of the two-stage, high-speed lining procedure when different speeds are used in the two stages, it can be employed for-simultaneously lining two molds by such a procedilre with both molds undergoing the two stages in succession without transfer from one set of rolls to the other.

After the moldhas been lined and faced at station 11, it is rolled along the rails 17 to the casting station 12 and provided with a bell socket core 45 and a spigot stopofi plate 46 of the character hereinafter described and illustrated in Fig. 7. The completed mold is then ready for casting. If, however, it is not needed for casting immediately, it may be left on the rails as long as desired without fear of deterioration because of the non-hygroscopic, selfsustaining character of the lining. In this connection, the length of rails 1'7 between stations 11 and 12 is preferably suflicient to accommodate all of the molds normally used in the system so that, whenever casting operations are suspended, all molds may be lined while still hot from their last casts and left ready for use when casting is resumed.

The apparatus at casting station 12 is substantially the same asthat heretofore used in centrifugal casting according to the Sandspun method, .and comprises two sets of mold rotating rollers 47 and 48 driven by a variable speed motor 49, a tiltable pouring ladle 50, a scale 51 for weighing the molten charge in the ladle and a relatively short pouring spout or trough 52 adapted to deliver the molten metal into the spigot end of the rotating mold. The ladle 50, scale 51 and spout 52 (all of which have been omitted from Fig. 2 in the interest of clarity) are mounted on a wheeled carriage 53 which is movable on rails 54 toward and away from the pouring position. The motor 49 may be automatically controlled in known manner by the mechanism which tilts the pouring ladle 50 so as to rotate themold at a relatively low speed while the major portion of the molten iron charge is being pouredand then rapidly accelerate it to a relatively high speed sufiicient to cast the poured metal centrifugally. Although the casting apparatus shown in Fig. 1 is adapted to pour the metal into the mold through the spigot end thereof, it will be understood that, in casting some sizes or types of pipe, it may be preferable to introduce the metal from the bell end of the mold, or even from both ends simultaneously.

After the casting operation has been completed, the mold with its contained solidified casting is ejected from the castin'g station 12 and rolled along the rails 17 to the stripping station 13. During this portion of the cycle, the bell socket core 45 and spigot stop-off plate 46 are removed from the ends of the mold and the heat of the cast metal completely burns out the resin binder of the mold lining, leaving the lining devoid of strength, so that the solidified pipe may be either pushed or pulled from the mold with relatively little effort. For the latter. purpose, the shipping station may be provided with a hydraulic ram 55 adapted to engage the spigot end of the cast pipe and push it out of the mold while axial movement of the mold itself is prevented by abutment of the bell end thereof against a suitable stop frame 56 having a central opening through which the pipe passes. When the bell end of the pipe has been forced out of the mold a suificient distance, it may be grabbed by a pipe puller mechanism (not shown) and dragged out of the mold onto a set-of rails 51 at station where the pipe isper mitt ed to cool and may be cleaned both externally and internally with wire bhist'ies any other sj'iiitabl manner. After cas ng an greening; the'pipes is may be left'dn rails 57 er tl'ilsf'erljed to any other Convenient Storage oiht, enning shipiiient; v v

After the fihislied'pipe hasbe'en stripped nomme tiiolti', the: ejnipty rr'ie tzil moid is rolled fi'otii the stripping station albiig the rails 17! to the elevator 18. As indicated in E2, the elevatof 18 is provided witha mold s'ilpportii'lg platform 58 tiltaply mounted at the upper end'of 5 hydi'aulic piston 59, th rails Hand 19 of the lower and runs, respectively, being provided with suitable step eis which cause the platform '58 to tilt into the same antes said so as to either receive or discharge the moldsby gravity. Whenthe elevator 18 is raised-to itsfupper'positiori, the empty mold carried on nephews rolls there froni ontothe rails 19 of the' u pper ruii and alongthe latter to the opposite etid'of the;systen'i' yi'heie lowered bythe drop and retui-ned to the lining d facing station 111011 rails 17'. The mold lowr ihg e drop 20 may bfo f any suitable coristriictitin, biit V i referably pneumatically controlled for descent and ceunter igliteu toretur it toraise'd position, and 5m- 'idei w t Pa r of; ver a l en n n r- 1 6i adapted to engage; and prevent the next mold in line from r oliihg oit the eiids or rails 19 while the mold in the drop ae er t As the hot, empty metal mold retu r ns along the rails 19' of theuppejr run; any sand that may remain therein from the lining of the previous cast may be blown out by compressed air or otherwise removed, and the ternperature of the mold is permitted to drop to within the range desired for the next lining operation. As previously indicated, artificial coolihg means may be incorporated the; return run in the event that the length thereof is iiisufiicient to produce the desired cooling under atmosphericj conditiohs; Also, if necessary, a manna-atii'lg station h'i'a y be added between the drop 20 and the lining and facing station 11, v v i The metal molds employed in practicing the new method embody certain features of novelty in comparison with those previously known which are claimed in chpending applicatioh Serial No. 348,952, filed April 15, 1 953. One formof such mold is shown in Figs. 4 9 of the accompanying drawings, which figures also illustrate the mold li'riin'g operation and the chaiacteristics of the rnoldas' it existslwhen ready for the casting step;

H Referring first to Fig. {1, which shows the metal mold before the resin bonded, s'arid lining has been formed, it will be seen that the mold is made up of threemain parts, an elohgatedbodyor center section 61 of substantially cylindrical form (the greater portion of which hasbeen broken away in Fig. 4),,a bell end section 62 which is threaded onto and weldedto one end of thebody 61, and

I a spigot end section 63 similarly threaded and welded to the oppos'ite end of the body. I v

The body section 61, which is preferably formed ofcast i'rnn with a wall thickness at least three times the thickness of the pipe to be cast therein, has an inside surface of uniform diameter, but on its outside is provided with twoenlarged cylindrical portions 64,, and 65, one adjaceint each end of the body, adapted to serve as spinning bands or tires for cooperation with the motor driven rollers of the lining' and facing station 11 and casting station 12 previously described. The body section 61 also has welded to its cr terion adjacent spinning band 64, an enlarged guide flange 66 whi h cooperates with a guide rail (not shown in Figs. 1-3) in known manner to properly position the mold in an axial direction with respect to the rollers of the rotating mechanisms at stations 11 and 12.. If desired, oneof the spinning bands may be grooved to receive the rollers of the rotating mechanisms andso located as to cooperate with theguide rail, in which event the guide flange 66 be omitted.

Thebell end sectoin 62 of the mold, which is prefetably made of cast steel, has an'inner cylindrical portion 67 which forms a prolongation of the body section 61 and an outer hopper portion 68 of outwardly flared, substantially frusto-conical form adapted to house a removable insert 69 for shaping the outer surface of the bell or flange end of the pipe to be cast in the mold. The insert 69 of the present invention is of relatively permanent character, being made of metal, either cast iron or steel, and is detachably held in place within the hopper 68 by means which insure accurate centering of the insert with respect to the rest of the mold and tight engagement between the inner end thereof and the abutting end of the inner cylindrical portion 67 of the bell end section 62.

As shown best in Fig. 8, the outer peripheral surface of the metal insert 69 conforms to the inner surface of the hopper portion 68 of the metal mold and has formed therein a plurality of radially extending recesses 70 equally spaced circumferentially of the insert, the outer portions of which recesses are cylindrical while the inner or bottom portions thereof are substantially conical, as indicated at 71. Each of recesses 70 is adapted to receive the similarly conical inner end 72 of a radially extending cap screw 73 which is threaded through the wall of the hopper 68. Inasmuch as the cylindrical and conical portions of each recess 70 are of greater diameter and depth, respectively, than the body and conical end of the cooperating screW 73, and the conical portion of the recess and the conical end of the screw are of the same angularity, it will be apparent that, as the screws are threaded inwardly and their conical ends 72 engage the conical bottoms 71 of the recesses, a wedging action will be exerted on the insert 69 which tends to force the latter axially inwardly and tightly clamp the outer periphery and inner end of the insert against the adjacent surfaces of the hopper 63 and inner cylindrical portion 67 of the mold end section 62. Accurate centering of the insert 69 with respect to the rest of the mold is additionally insured by shouldering or rabbeting the inner end of the insert and the abutting end of cylindrical portion 67 of bell end section 62, as indicated at 74.

The inner circumferential surface of insert 69 may have any desired shape, depending upon the form which it is desired to impart to the corresponding end of the cast pipe, but is such that, when the insert is in place, said surface forms a smooth continuation of the inner cylindrical surface of portion 67 of bell end section 62 which in turn constitutes a prolongation of mold body section 61. In practice, each insert 69 is interchangeable with a number of others having different inside contours. Since the mold lining method of the present invention results in a smooth, dense refractory lining over the entire interior surface of the mold, including the insert 69, the joint between the inner end of the latter and the mold body is effectively covered by the lining and leaves no mark on the outside surface of the casting.

The outer end of hopper portion 68 of the mold is provided with a substantially cylindrical rim 75 wherein are formed a plurality of circumferentially spaced, radial ly extending holes 76 adapted to receive wedge-shaped keys 77 which are driven into said holes from the inside of the rim so that, when the mold is rotated, centrifugal,

force tends to force the keys even tighter into the holes. The keys 77 engage and hold in place against the outer end of insert 69 either the annular lining stop-off plate 37 shown in Fig. 4 when the latter is used during the lining operation, or the bell socket core 45 shown in Fig. 7 which is used during the casting step.

Although the use of interchangeable, permanent metallic inserts 69 results in certain obvious advantages, it will be apparent that ordinary sand insert cores might be used instead, if desired, in which case the cap screws 73 could be eliminated and the sand cores held in place by the wedge keys 77.

The spigot end section 63 of the metal mold is also preferably made of cast steel and consists of a substantially cylindrical prolongation of center section 61 having at its outer end a radially extending flange 78 forming a convenient means for detachable connection to the mold of the lining stop-off plate 36 of Fig. 4 and the casting stop-off plate 46 shown in Fig. 7. In each case, the stopoff plate is provided with a plurality of axially extending stud bolts 79 adapted to pass through holes in the flange 78 and receive nuts 80 which secure the plate to said flange. While the inner surface of lining stop-off plate 36 is smooth so as to form a square edge at the end of the mold lining, the corresponding surface of casting stop-01f plate 46 is provided with an annular groove 81 which faces the spigot end of the pipe to be cast in the mold (indicated in broken lines in Fig. 7) and is filled with a quantity of resin bonded sand of the same composition as the mold lining which serves to prevent chilling of the end of the casting. It is also preferable to face the bonded refractory filling of groove 81 with the same blacking as that applied to the mold lining.

Instead of dividing the metal mold into three sections as shown, it is obvious that the cylindrical portions 61, 63 and 67 may be made in one piece with a separately formed hopper portion 68 threaded and welded thereto, or, alternatively, that the entire mold may be machined from a single casting.

In pursuance of the advantages resulting from the use of vented molds, an improved form of vent has been devised which is particularly effective with the mold lining procedure of the present invention. As indicated in Figs. 4-7, the metal mold is provided with a relatively large number of uniquely constructed vents, indicated generally at 82, constituting openings through the mold wall for escape of the gases formed during casting. The vents 82 are distributed more or less uniformly over the entire length of the mold, with the exception of the hopper portion 68 and the spinning band portions 64 and 65. The number and positioning of the vents should be such as to permit ready escape therethrough of substantially all of the gas generated during the casting operation, and will depend upon a number of factors such as the thickness of the lining, the percentage of resin binder therein, the grain size of the lining sand, the character and thickness of the facing on the lining, and the temperature of the metal being cast. As an example, it has been found that, in a mold for casting a 6 cast iron pipe 20 feet long, four axially extending rows of vents located 90 apart with a spacing of approximately 3.7" between adjacent vents in the same row, the vents in adjacent rows being staggered, will be adequate under all normal conditions of lining thickness, amount of resin binder, etc.

As shown best in the enlarged view of Fig. 9, each vent 82 consists of a radially extending hole drilled through the mold wall having an outer portion 83 of uniform diameter which extends inwardly from the outer surface of the mold almost to the inner surface thereof, and a relatively short inner portion 84 of substantially smaller diameter which opens into the interior of the mold, the shoulder 85 connecting the outer and inner portions of the hole preferably being inclined as shown, rather than square. While the length of the outer portion 83 will vary with the thickness of the mold wall, it is desirable to limit both the length and the diameter of the inner portion 84 to approximately /8, and to make the diameter of the outer portion 83 approximately three times that of the inner portion.

When a metal mold having vents of this character is lined according to either the single stage, two-speed technique or the one-step, uniform speed procedure of the present invention, the inner portions 84 of the vent holes eminent) l7 ties melts and'polyi'nerizesvery quickly and rapidly fuses the sand grains together in a rigid, :gas permeable mass, and also "cements said mass to the surrounding wall of the inner portion 84 of the "venthole, "before the liningindi- 'cated 'at 86 in '-Fi'g. 9 is formed. After this preliminary closure of the ventholes, the-mold lining 86 forms in'un'iform manner over theent'ire interior ofthe mold and provides an additional coating over the -inner ends of the vents of the 'same'thickness"and density'as the restof the lining.

lnsOrne cases, particularly when relatively-fine sand or a relatively small percentage of resin is'used'in the'lining, or when the liningis formed by the two-stage,'high-speed method, it is desirableto take'special steps'to-pre'vent the possibility of escape of the sand-resin lining mixture through the vent holesduringthe liningoperationa To this'end, as shown in Fig. 10, the-outer portion '83 of each vent may be packed with a quantity of unbonded, relatively coarse granular refractory 87,'such 'as-sand o'f a'size that will notpass through a /8" mesh screen. 'In order to hold the packing in place, a cup-"shaped metal corebox vent 88,'having.aplurality-of perforations *89in 'the bottom thereof, may be fixedin the outer end of the vent-hole, as by peening. With this arrangement, the gases generated in the lining during casting can freely escape through the porous refractory mass 87 and the perforations 89xof the core box vent 88, while :the refractory packingand core box vent effectively prevent the lining mixture from being thrown out through the vent hole un'dercentrifugal :force. It will be understood that,'in this .inodificatiomthepacking 87 and core box vent 88 are relatively permanent parts of the mold, it being unnecessary to :renew the packing for each cast, but only at such timeslasit isdesired'to thoroughly-cleantthe vents.

There .is thus provided by the present invention anew and improved method for 'centrifugally casting .hollow metal articles :of cast iron, steel or non-ferrous metals which is particularly well adapted .to the production *of pipe, especially pipes having belled-orfiangedends. The

of castings withaniinirnurn \of eguipmentand .manual labor, and produces .high .quality, clean castings to close tolerances and of anyreasonable shape and-size.

While the castings madein accordance .withthepresent procedure have all of the advantageous characteristics of those made in conventional .sand .molds, (including .an unchilled, close grain structure .free from inclusions, the improved methodof centrifugally'liriing metalmolds with a relatively thin, resin lbonded refractory coating avoids such disadvantages of thepriorSandspun procedureas the necessity for manually ramminga relatively thick green sand lining around a pattern with the aid of expensive machinery, "the use of a large amount of 'sand'and "sand handling equipment, and the need for expensive cutting mechanism or other means for removing the sand lining from between'the flask and thecast'ing before the latter can be strippedfromihemold. Thefasterfreezing of the cast metal with the relatively :thinner :mold lining .provided by the present invention, as well "as the fact .that the relatively lighter .weight'of .the molds enables quicker acceleration of their rotation :during the casting step, resultin an increased productionvratesin cornparison with the sand .mold process of the prior art. The new .pro- 'cedurelikewise embodiesmost of the advantages of the old de 'Lavaudrmethod employingmeta'l molds, but without such disadvantages thereof as the excessive wear and cracking of the molds due to contact with the molten metal, andthe'necessity' for annealing'the chilled castings produced by said method.

Although certain examples have been given of the procedural steps .of :the method .and one specific sembodiment of apparatus .for performing .the method 1188 been described and illustrated in the accompanying drawings, it will be-obvious thattthe invention-is notlimitedtothese illustrativetexarnples or to-theparticular apparatus shown, but that various changes, which will now suggest them- '18 rslves to those skilled in the art, may hematite in both the method and "the "apparatus without "departing from "the'inventive concept. Reference is there'foretobe had to .the appended claims for a definition o'fthe limits 'of "ihe'invention.

This application is "a continuation-impart of abandoned application Serial 'No. 21 2,468,'-fi1ed February '23, "1951.

What is claimed is:

'1. A method "of making hollow metal castings of gen- :erally cylindrical form in rotatable vented molds comprising the steps of providing a rotatable Yhollow metal mold having vents in the wall "-ithere'of and -having said wall heated to a temperature within the "range from 300 to 600 'F., forming arefractory lining of "predetermined "thickness'in:said metalmdld' by' dliveringinto the interior thereof :anneasured quantity of loose, dry granular refractory-thermosetting resin material calculated to provide a lining of the desired lthick'ne'ss, :uniformly "distributing 'said material longitudinallyof'ithe mold and fusing said material intoastrongly bondedlining adherent to't'he mdld wall by the "use of heat' 'extra'cted from said will while rotating said mold about :a substantially horizontal axis .to uniformly distribute "the material :circurnferentially over :the'inner surface :of thermold, introducing-a charge'of molten metal -into ens lined *mold "while rotating the latter :about .a substantially' horizontal axis, continuing said rota- .tion until thermetal has solidifiedputilizing'the'heat of said metal to burn outt'he :resin in -:the 'm'o'ld lining and thereby destroy the bond bet-we'en the refractory granules and "the adhesion of said granules itothe'wallof the mold while :the gases "produced in said Llining by 'the heat of said metal escape outwardly through tthe vents in the mold .---wall, stripping ithe' solidified metal oasting from "the mold,

and relining the .mold while the wall there'of retains su'ffizcientcheat .fromthe casting to fuse the refractory-resin :material of the mew liriirrg.

2. A method of making -:cast iron pipe in rotatable vented molds comprising thestepsof providing arotatable hollowmetal tnrold hav ing vents in {the wall thereof and Ehaving asaid wall hea'te'd =10 a temperature =witliin the range from 300 to 600 F., forming a refractory lining ofpredetermined fthi'ckncss iin ssa'id mold by delivering into the :interior' the'reof 2a measured quantity of loose, "dry :silica sand calculated ito provide a Flining of "the desired thickness and thriving mixed tlrerewith a :srna'll proportion of Ithermosetting res'in, luniformly distributing *the sandresin mixture longitudinally of the mold and fusing 'said inixturerinto: ais'trong'lyIbondedlining'adherent to the mold wall iby the use or heat extracted from said wall while rotating :said mold iaboutaa substantially horizontal axis :to 'uniformly'dis'tribute iith'ezmix'ture circurnferentially over the inner surface 'ofithelmdld, applying a carbon facing to thedining-oflsaidimoldppouring a charge o'fmolteniron 'into'theflinedvmoldwhilemotating the letter about a substantially horizontal axis, continuing said rotation until the firon has :solidified, utilizing the 'heat of said iron to .burn out the T'ICSil'l in the mold lining and thereby destroy the bond between the sand granules and -'the adhesion of saidggranuleszto'the wallcofithe mold while-the 'gases produced in said lining by :the :heat of :said metal "esc'ape ou'twardly through the events in .the mold wall, istripping rth'e solidified iron casting from .the mold, and rrelinin'g the mold .while the wall thereof metains sufficient heat from the casting to fuse the sand-resin :mixture of the .new lining.

3. A method of centriiugally wasting tubular unetal articles-of the type'wherein a charge of molten metal fis introduced into :a arefractory dined :metal :mold while tth'e mold is rotating about :a substantially horizontal axis, characterized @by ithe steps iof;providing iarotatable rhollow metal =n1old=having tvents in the wall ihereoisand said mold with a material composed nf .a :granular refrac- .tory .and La rthermosetting "resin 'iwhile .:rotating said unold to uniformly distribute the -lining material ecircumferentially over the inner surface of the mold and maintaining its 19 temperature within the range from 300 to 600 F. so that the heat of the mold fuses the refractory-resin material into a strongly bonded coating adherent to the inner surface of said mold. I

4. The method defined in claim 3 wherein the lining material consists essentially of from 95.0 to 99.5% by weight of silica sand and from 0.5 to 5.0% by Weight of a fusible phenolic resin.

5. The method defined in claim 3 wherein the lining material consists essentially of from 95.0 to 98.5% by weight of dry silica sand and from 1.5 to 5 .0% by weight of a powdered thermosetting resin.

6. The method defined in claim 3 wherein the lining material consists essentially of silica sand having a coating of thermosetting resin, the resin content of the sand coating being from 0.5 to 5.0% of the weight of the coated sand. 1

7. A method of centrifugally casting tubular metal articles of the type wherein a charge of molten metal is introduced into a refractory lined metal mold while the mold is rotating about a substantially horizontal axis, characterizedby the steps of providing a rotatable hollow metal mold having vents in the wall thereof, heating said mold to a temperature within the range from 300 to 600 F., distributing uniformly along the axis of said mold a measured quantityof a loose, dry lining material consisting essentially of silica sand and a thermosetting resin, rotating said mold about its axis to uniformly distribute the particles of said material circumferentially over the inner surface of said mold, and continuing the rotation of said mold until said particles have been fused together to form a hard refractory lining adherent to the mold wall under. the effect of the :heat of said wall on the thermosetting resin.

8. The method defined in claim 7 wherein the resin content of the lining material is from 0.5 to 5.0% of the total weight of said material.

9. The method defined in claim 7 including the additional step of applying a carbon-containing facing to the inner surface of the resin bonded sand lining of said mold. p

10. A method of centrifugally casting hollow'metal bodies of the type wherein a charge of molten metal is introduced into a refractory lined metal mold while the mold is rotating about a substantially horizontal axis, characterized by the steps of delivering into the interior of a hollow metal mold having vents in the wall thereof a measured quantity of loose, dry refractory-thermosetting resin material calculated to provide a lining of predetermined thickness, distributing said material uniformly along the axis of said mold while rotating said mold at a relatively low speed, insufiicient to hold the particles of said material to the mold wall by centrifugal force, and while maintaining the temperature of said mold wall within the range from 300 to 600 F., continuing the low-speed rotation of said mold until the particles begin to adhere to the mold wall due to the effect of the heat of said wall onthe thermosetting resin, and then rotating said mold at a substantially higher speed, sufiicient to hold theremaining loose particles of said material to the mold wall by-centrifugal force, until substantially all of the resin has polymerized and bonded the particles-together to form a relatively smooth, 'hard liningadherent to the'mold wall. i i

11. The method defined in claim 10 wherein the relatively low speed of rotation of the mold is such that the centrifugal force created at the inner surface of said mold is not more than about 0.5 times the force of gravity, and the substantially higher speed is such that the centrifugal force created at the inner surface of said mold is not less than about 5.0 times the force of gravity.

12. A method of centrifugally casting hollow metal bodies of the type wherein a charge of molten metal is introduced into a refractory lined metal mold while the mold is rotating about a substantially horizontal axis, characterized by the steps of heating a hollow metal mold having vents in the wall thereof to a temperature within the range from 300? to 600 F., rotating the heated mold about a substantially horizontal axis at a relatively low speed such that the centrifugal force created at the inner surface of said mold is not more than about 0.5 times the force of gravity, delivering into said rotating mold a measured quantity of loose, dry granular refractory-thermosctting resin material calculated to provide a lining of predetermined thickness, distributing said refractory-resin material uniformly along the axis of said mold, continuing the low-speed rotation of said mold to uniformly distribute the refractory granules circumferentially over the inner surface of the mold and until said granules have been fused together to form a hard refractory lining adherent to, the mold wall under the effect of the heat of said wall on the therrnosetting resin, and then applying'a carbon-containing facing to the inner surface of said mold lining while rotating the mold at substantially the same speed as that atwhich it was rotated during the lining operation.

13. The method defined in claim 12 wherein the carbon-containing facing consists essentially of a dry mixture of relatively fine sand, ground coke and a thermosetting resin.

14. The method defined in claim 12 wherein the carbon-containing facing is applied to the mold lining by blowing into the lined mold a dry mixture of from 33 to 50%.by weight of relatively fine silica sand and from 50 to 67 by weight of ground coke, plus an amount of thermosetting resin equal to from 8 to 12% of the total weight of the sand and coke.

15. A method of centrifugally casting hollow metal bodies of the type wherein a charge of molten metal is introduced into a refractory lined metal mold while the mold is rotating about a substantially horizontal axis, characterized by the steps of delivering into the interior of a hollow metal mold having vents in the wall thereof a measured quantity of loose,"dry refractory-thermosetting resin material calculated to provide a lining layer of predetermined thickness, distributing said material uniformly along the axis of said mold While rotating said mold at a relatively high speed, sufficient to hold the particles of said material to the mold wall by centrifugal force, and while maintaining the temperature of said mold wall within the range from 300 to 600 F.,continuing the high-speed rotation of said mold until said particles have been fused together to form 'a hard refractory lining layer adherent to the mold wall under the effect of the heat of said wall on the thermosetting resin, then delivering into the interior of the partially lined mold a second measured quantity of loose, dry refractorythermosetting resin material containing a small proportion of graphite While rotating said mold at a speed higher than the speed employed during formation of the first lining layer, and continuing said rotation until the particles of said second quantity of lining material have been fused together to form a second hard refractory lining layer adherent to said first layer.

16. The method defined in claim 15 wherein the refractory-resin material used for forming the first lining layer contains from 0.5 to 5.0% by weight of a fusible phenolic resin, and the mixture used for forming the second lining layer contains from 0.5 to 5.0% by weight of a fusible phenolic resin and a substantially equivalent amount of graphite. Y

17. The method defined in claim .15 wherein the refractory-resin material used for forming the second lining layer also contains a small amount of iron oxide.

18. The method defined in claim 15 wherein the speeds at which the'mold-is rotated during formation of said first and second lining layers are such that the centrifugal less than about 50 times the force of gravity.

References Cited in the file of this patent UNITED STATES PATENTS Whitley Mar. 15, 1887 Moore et a1. Mar. 15, 1927 Langenohl et al. Apr. 22, 1941 Barr June 17, 1941 Projahn et a1. July 14, 1942 Ritchie Sept. 8, 1942 Boucher Mar. 14, 1944 Schuh et al. Apr. 30, 1946 Pattison Sept. 14, 1948 Higgens Oct. 5, 1948 22 Olsen et al. Aug. 8, 1950 Johnston July 3, 1951 Johnston May 27, 1952 Myers Dec. 30, 1952 Romine Mar. 17, 1953 Burchartz July 14, 1953 Cito Dec. 29, 1953 Samuels Sept. 28, 1954 OTHER REFERENCES Modern Metals October 1950, pages 22-24. Fiat Final Report No. 1168, The C Process of Making Molds and Cores for Foundry Use. Published May 30, 1947, by Ofiice of Technical Services, Dept. of Com- 15 merce, Washington, D. C., 10 pages. 

3. A METHOD OF CENTRIFUGALLY CASTIN TUBULAR METAL ARTICLES OF THE TYPE WHEREIN A CHARGE OF MOLTEN METAL IS INTRODUCED INTO A REFRACTORY LINED METAL MOLD WHILE THE MOLD IS ROTATING ABOUT A SUBSTANTIALLY HORIZONTAL AXIS, CHARACTERIZED BY THE STEPS OF PROVIDING A ROTATABLE HOLLOW METAL MOLD HAVING VENTS IN THE WALL THEREOF, AND LINING SAID MOLD WITH A MATERIAL COMPOSED OF A GRANULAR REFRACTORY AND A THERMOSETTING RESIN WHILE ROTATING SAID MOLD 